Pressure Ferment- SG Flat, but Still Airlock Activity

[micraftbeer]

I'm newer to fermentation under pressure. I've seen this same phenomenon before, and wondered the same question of whether the beer was finished or not. In this case, the beer fermented quicker than expected, and I'm fiddling around with pressure, so not sure if that affects how I'd interpret this or not. I know I can let it ride and no harm will come, but I am very curious to see how quickly I can turn this beer around just for research's sake of using pressurized fermentation to naturally carbonate.

I made a wheat beer with a lot of wheat (59% red wheat malt + 7% flaked wheat), and am fermenting with Imperial A07 Flagship yeast (which is a Chico strain). I started fermentation with no pressure, then after a day, I dialed the spunding up to 5 psi. When I was what I estimated to be 90% to my FG, I cranked up the spunding to 29 psi to let it build pressure and naturally carbonate. Everything went fine overall, I just got to a flatline SG on my Tilt much sooner than I expected.

Of course, if you've used Tilts, you know their actual measurement value has to be taken with a grain of salt, and just focus more on tracking trends, and rate of change of SG. So in hindsight, I dialed it up to 29 psi when it had more than 10% to go to FG. But if anything, that should've slowed down fermentation and prevented it from flatlining as soon. But it reached the point I'm calling "flatline" at just under 3 days from yeast pitch. And I was fermenting most of this at 68F, only adding some heat until I was at around that flatline point. I've now been at this flatline for a little over 2 days, but I continue to see bubbling in the spunding output (currently at about every 8 seconds).

At this point, I'm thinking I'll just sit and wait until it stops bubbling AND has been at the flatline portion of SG for 3 days. But I'm interested in opinions on this. Plot below...

 

[GilSwillBasementBrews]

Bubbling in airlock or spunding dump is not an indication of fermenting. Pressure and temp changes will cause air locks to bubble.

 

[Craiginthecorn]

Since you have been fermenting at a very high pressure (15 psi is the highest I've seen recommended due to yeast stress), you will have quite a bit of dissolved CO2 -- about 2.5 volumes at 70F. This can somewhat affect your Tilt's readings. I would guess in the neighborhood of .004-.005 SG.

It would be interesting to get either an alcohol-corrected refractometer reading it a degassed hydrometer reading. If you do get one of these, please share that reading and the current Tilt reading.

 

[micraftbeer]

I'm in the process of cold crashing now (fermentor sitting in my beer fridge). I decided that based on the SG flatline for several days, the small bubbles I'd get in the "spunding blowoff" every 8 seconds or so was some other phenomenna. I pulled a sample and will let this sit out and go flat and I'll get a refractometer reading on it (I ditched those dump fragile, hard-to-read hydrometers a long time ago)- and plug it in to the alcohol corrector.

As for the pressure, if you read through my OP, you'll see I had a specific method to my madness. I started the first 20 hours of ferment with no pressure, then kept it low at 5 psi through the majority. At the tail end, I ramped up the pressure to 29 psi in order to let the final yeast conversion work carbonate the beer for me. I did that only at the end because I as well have read the Blichmann/White Labs experiment where they compared the pressures with tastings. So I'm trying to get the best of both worlds, or cake and eat it type situation here.

The challenge with this method is that us Tilt users know that the FG reading on the Tilt is usually high or low vs. reality. So trying to ramp up to 29 psi for the last 10% of SG drop can be tricky.

 

[khannon]

Think about what would happen if you put an airlock on a bottle of beer you got from the store.. You would see bubbles come out as pressure equalized and the beer went "flat".

 

[micraftbeer]

The difference here is the spunding valve. The spring inside the valve pushes against the diaphragm inside of it. If the pressure of the beer can't overcome the spring force, all of the gas stays trapped inside. And no bubbles.

If the pressure inside gets high enough to overcome the spring, it pushes the diaphragm up, and then some pressurized air/CO2 slips out.

A regular airlock with 2 inches of water would have 0.07 psi pressure to overcome (2.31 feet of water creates 1 psi). So your beer would go flat in that situation as all of the CO2 would work its way out.

 

[Craiginthecorn]

The challenge with this method is that us Tilt users know that the FG reading on the Tilt is usually high or low vs. reality. So trying to ramp up to 29 psi for the last 10% of SG drop can be tricky.

I think you may be overcomplicating this. If your goal is solely carbonation, then the concern is putting on the spunding valve too late, rather than too early. If you were attempting to carbonate naturally by closing the fermenter without using a spunding valve, then yes, timing it would be tricky, even with a hydrometer, as you would need to know the precise finishing gravity as well. But with a spunding valve the timing is easy. Almost anytime would work, as long as there’s enough unfermented sugar left. The spunding valve let’s out any excess CO2.

 

[micraftbeer]

What I mean by tricky is this. As you've mentioned, the guidance is you don't want to ferment the whole thing at 29 psi from a flavor perspective. So I want to dial up the pressure as late as possible, for the least risk of flavor impact. But I want to dial it up early enough to get my 2.4 vols of CO2.

Being able to hit that sweet spot, I need to know how many more points of SG I'm going to drop. So with my experience of FG with the Tilt being higher or lower than my final measured FG, that's the challenge.

 

[micraftbeer]

I'm in the process of cold crashing now (fermentor sitting in my beer fridge). I pulled a sample and will let this sit out and go flat and I'll get a refractometer reading on it

1.011 refractometer reading after correction for OG.

 

[VikeMan]

Since you have been fermenting at a very high pressure (15 psi is the highest I've seen recommended due to yeast stress), you will have quite a bit of dissolved CO2 -- about 2.5 volumes at 70F.

15 PSI at 70F hits equlibrium at about 1.64 volumes. To get 2.5 volumes, you'd need almost 29 PSI.

Edit: I see now you were referring to the OP's 29 PSI and not to 15 PSI. Carry on.